1. Field of the Invention
The present invention relates to a semiconductor memory device which includes a circuit including a semiconductor element such as a transistor, and a driving method thereof.
2. Description of the Related Art
A dynamic random access memory (DRAM) is a semiconductor memory device where one bit of data can be stored with use of one transistor and one capacitor. The DRAM has advantages such as a small area per unit memory cell, easiness in integration for modularization, and low manufacturing cost.
The DRAM requires an operation of recharge (refresh) before necessary electric charge is lost. A counter of a memory controller or a microcomputer incorporating a memory controller counts timing for performing a refresh operation, and the refresh operation is performed when the count becomes a predetermined value.
Since frequent refresh operations increase power consumption, reduction of the frequency of the refresh operations has been attempted (see Patent Document 1).